1. Field of the Invention
The present invention relates to a target follow-up device which follows up a predetermined target in the photographic field of an imaging device such as a camera or the like, and also relates to a camera equipped with such a target follow-up device.
2. Description of the Related Art
Such a type of target follow-up device has for example been described in Japanese Patent Publications 60-33350 and 61-19076. In these prior art devices, the correlation coefficient between a previously stored reference image and an input image obtained by A/D conversion of a picture signal supplied by an imaging device is calculated, and the predetermined target is followed up by determining which coordinates yield the maximum value of this correlation coefficient. In this case, with the intention of being able to perform follow up action in real time, a region for calculation of the correlation coefficient is established in the photographic field, and the calculation of the correlation coefficient with the reference image is performed over this region.
Further, there is a per se known type of device (for example, refer to U.S. Pat. No. 5,031,049) which follows up a target (the object to be photographed) within the photographic field by detecting a color difference signal over the photographic field, recording this color difference signal over a designated area (the area which the photographer designates as containing the principal target), comparing this recorded color difference signal with the color difference signal in the periphery of the designated area, and thereby determining to what position within the photographic field the principal target has moved.
Nevertheless, with these prior art type target follow-up devices, since the region for correlation calculation either was set by taking as its center the position of the target as determined in the previous iteration of the target follow-up process, or simply was a fixed area within the photographic field of view, therefore there has been a risk that, when photographing a sports scene or the like containing a target which is moving very quickly, the target may move out of the region for correlation calculation, which causes problems with regard to following up the position of the target. Further, when the shape of the target changes quickly, as again can easily occur when photographing a sports scene or the like (for example, when the target rotates quickly from a full frontal aspect to a profile aspect), or when the brightness of the target changes quickly (for example when it moves from a sunlit area to a shaded area), then in some cases it becomes impossible to perform accurate target follow-up by calculation of the correlation coefficient with reference image data recorded in advance.
Further, up to the present no camera has existed in which the operation of the above type of target follow-up device has been organically correlated with photographic modes, focus detection modes, or auto zoom modes of the camera.
Now, the expression "photographic mode" is used in this specification in the following manner, for example: the most suitable mode of exposure control for performing sports photography is termed the "sports photography mode", the most suitable mode of exposure control for performing portrait photography is termed the "portrait photography mode", etc. Further, the expression "focus detection mode" is used in this specification in the following manner, for example: a mode in which focusing adjustment movement of the photographic lens is repeatedly performed based upon the output of a focus detection device is termed the "continuous mode"; a mode in which, when once based upon the output of a focus detection device the condition in which of the photographic lens is on focus is detected, afterwards the driving of the photographic lens is forcibly stopped is termed the "one shot mode", a mode in which the focus can be independently detected for a plurality of regions in the photographic field of view based upon the output of a focus detection device is termed the "multi mode", etc. Further, with an automatic zoom lens, there are so called "auto zoom" modes like one in which the zoom lens is automatically driven so as always to maintain a photographic magnification determined in advance, even in the event of change in the photographic distance or the like, etc.